Carrier-Selective NiO/Si and TiO₂/Si Contacts for Silicon Heterojunction Solar Cells

Recent Advances in and New Perspectives on Crystalline Silicon Solar Cells with Carrier-Selective Passivation Contacts

“…Alternative materials are expected to completely replace doped silicon layers to form the asymmetric carrier selective heterocontacts with c-Si wafers. These alternative materials, which usually are called carrier-selective materials or passivation contact materials, include transition metal oxides [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], organic materials [48][49][50][51][52][53], and alkali/alkaline earth metals and/or salts [30,40,[54][55][56][57][58][59][60][61]. Compared to doped-silicon layers, dopant-free carrier-selective materials open a wider optical and electrical parameter space, decoupling the optimization of different solar cell loss components.…”

“…Compared to the doped silicon films, dopant-free carrier-selective contacts consist of elementary or compound thin films, with high work functions as hole-selective contacts and low work functions as electron-selective contacts. For example, electron-selective contacts include compounds with a low work function, such as LiF x [30,32,40], MgF x [56], TiO 2 [31,40,[43][44][45] and ZnO [46,47], and alkaline metals with an extremely low work function, such as Mg [54] and Ca [57]. Hole-selective contacts mainly consist of organic films [48][49][50][51][52][53] and transition metal oxides (TMO s ), such as MoO x [30,32,[36][37][38][40][41][42]47], WO x [35,38,39] [33][34][35]38], and NiO x [31].…”

“…Inherited from the organic electronic community, thin alkali and alkaline earth metal salt interlayers, including LiFx [30,32,40], MgF x [56], Mg [54] and Ca [57], can be used to enhance electron extraction, and when these layers are integrated under a metal electrode, low work function values can be obtained (as low as~2.5 eV, in some cases), promoting electron collection from the adjacent c-Si surface. In fact, alkali and/or alkaline earth metal salts have been explored intensively as electrodes with low work functions in solar cells and light-emitting diodes.…”

Toward Annealing‐Stable Molybdenum‐Oxide‐Based Hole‐Selective Contacts For Silicon Photovoltaics

“…The use of passivating contacts—like the ones used in silicon heterojunction (SHJ) solar cells—suppresses these recombination routes by separating the metal from the surface of the Si wafer and omitting heavy doping of the Si wafer. To reduce further the optical losses in passivating contacts, the application of wide‐bandgap materials like molybdenum‐, tungsten‐, titanium‐, or nickel‐oxide (MoO X ,, WO X , TiO 2 , NiO ), as well as lithium‐ or magnesium‐fluoride (LiF, MgF 2 ) has received much attention in recent years. These materials feature a work function that is either higher than the ionization energy, or lower than the electron affinity of crystalline Si (c‐Si).…”

Silicon Heterojunction Solar Cells with MoOx Hole‐Selective Layer by Hot Wire Oxidation–Sublimation Deposition

“…Differences between the work functions of the metal oxides and Fermi levels of the c‐Si lead to a large energy band bending of the c‐Si near the interface, which allows only one type of carrier to pass through and inhibits carrier recombination at the interface . Some metal oxides with high work functions, such as MoO x , VO x , WO x , NiO x , and CuO x , can provide good hole‐selective transport when they form heterocontacts with c‐Si. Similarly, some metal oxides with low work functions, such as TiO x , MgO x , and ZnO, can be used as the electron‐selective transport layers instead of n‐type a‐Si:H in c‐Si solar cells.…”